feat(matplotlib): implement streamline-basic (#2904)

## Implementation: `streamline-basic` - matplotlib

Implements the **matplotlib** version of `streamline-basic`.

**File:** `plots/streamline-basic/implementations/matplotlib.py`

**Parent Issue:** #2861

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:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20608630642)*

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Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]

plots/streamline-basic/implementations/matplotlib.py

@@ -0,0 +1,47 @@
+""" pyplots.ai
+streamline-basic: Basic Streamline Plot
+Library: matplotlib 3.10.8 | Python 3.13.11
+Quality: 93/100 | Created: 2025-12-31
+"""
+
+import matplotlib.pyplot as plt
+import numpy as np
+
+
+# Data - Create a vortex flow field
+np.random.seed(42)
+
+# Grid setup (40x40 for smooth streamlines)
+x = np.linspace(-3, 3, 40)
+y = np.linspace(-3, 3, 40)
+X, Y = np.meshgrid(x, y)
+
+# Vortex flow field: u = -y, v = x (creates circular streamlines)
+# Add a second vortex offset to show more interesting flow patterns
+U = -Y + 0.5 * np.exp(-((X - 1.5) ** 2 + Y**2))
+V = X + 0.5 * np.exp(-((X + 1.5) ** 2 + Y**2))
+
+# Calculate velocity magnitude for color mapping
+speed = np.sqrt(U**2 + V**2)
+
+# Plot
+fig, ax = plt.subplots(figsize=(16, 9))
+
+# Create streamlines with color based on velocity magnitude
+strm = ax.streamplot(X, Y, U, V, color=speed, cmap="viridis", linewidth=2.5, density=1.5, arrowsize=2, arrowstyle="->")
+
+# Colorbar for velocity magnitude
+cbar = fig.colorbar(strm.lines, ax=ax, shrink=0.8, pad=0.02)
+cbar.set_label("Velocity Magnitude", fontsize=20)
+cbar.ax.tick_params(labelsize=16)
+
+# Styling
+ax.set_xlabel("X Position", fontsize=20)
+ax.set_ylabel("Y Position", fontsize=20)
+ax.set_title("streamline-basic · matplotlib · pyplots.ai", fontsize=24)
+ax.tick_params(axis="both", labelsize=16)
+ax.set_aspect("equal")
+ax.grid(True, alpha=0.3, linestyle="--")
+
+plt.tight_layout()
+plt.savefig("plot.png", dpi=300, bbox_inches="tight")

plots/streamline-basic/metadata/matplotlib.yaml

@@ -0,0 +1,26 @@
+library: matplotlib
+specification_id: streamline-basic
+created: '2025-12-31T00:07:17Z'
+updated: '2025-12-31T00:11:24Z'
+generated_by: claude-opus-4-5-20251101
+workflow_run: 20608630642
+issue: 2861
+python_version: 3.13.11
+library_version: 3.10.8
+preview_url: https://storage.googleapis.com/pyplots-images/plots/streamline-basic/matplotlib/plot.png
+preview_thumb: https://storage.googleapis.com/pyplots-images/plots/streamline-basic/matplotlib/plot_thumb.png
+preview_html: null
+quality_score: 93
+review:
+  strengths:
+  - Excellent use of matplotlib's streamplot with color-mapped velocity magnitude
+  - Clean, readable code following KISS principles
+  - Viridis colormap ensures colorblind accessibility
+  - Proper title format and well-sized text elements
+  - Vortex flow pattern clearly demonstrates streamline concept
+  - Good use of equal aspect ratio for proper visualization of circular flow
+  weaknesses:
+  - Axis labels lack units (could be "X Position (m)" or similar)
+  - Grid linestyle dashed is slightly more visible than needed
+  - Could use linewidth varying with speed for additional visual encoding
+  - Flow field could be more complex (e.g., dipole) to show more features